Substitution Templates

You can use a substitution template to augment the JSON data returned when a rule
is triggered and AWS IoT performs an action. The syntax for a substitution template
is
${expression}, where
expression can be any expression supported by AWS IoT in a
SELECT or WHERE clause. This includes functions, operators and information present
in
the original message payload. However, you cannot reference an alias created using
the
AS clause (because an expression in a substitution template is evaluated separately
from the "SELECT ..." statement). For more information about supported expressions,
see
AWS IoT SQL Reference.